Spray drying is a well known and extensively used process in which liquid slurries are sprayed into a drying chamber into which heated air is introduced for drying the liquid into powder. The slurry commonly includes a liquid, such as water, an ingredient, such as a food, flavor, or pharmaceutical, and a carrier. During the drying process, the liquid is driven off leaving the ingredient in powder form encapsulated within the carrier. Spray drying also is used in producing powders that do not require encapsulation, such as various food products, additives, and chemicals.
Spray drying systems commonly are relatively massive in construction, having drying towers that can reach several stories in height. Not only is the equipment itself a substantial capital investment, the facility in which it is used must be of sufficient size and design to house such equipment. Heating requirements for the drying medium also can be expensive.
While it is desirable to use electrostatic spray nozzles for generating electrically charged particles that facilitate quicker drying, due to the largely steel construction of such sprayer dryer systems, the electrostatically charged liquid can charge components of the system in a manner, particularly if unintentionally grounded, that can impede operation of electrical controls and interrupt operation, resulting in the discharge of uncharged liquid that is not dried according to specification.
While it is known to form the drying chamber of electrostatic spray dryers of a non metallic material to better insulate the system from the electrically charged liquid, particles can adhere to and build up on the walls of the drying chamber, requiring time consuming cleanup which interrupts the use of the system. Moreover, very fine dried powder within the atmosphere of heating air in the drying chamber can create a dangerous explosive condition from an inadvertent spark or malfunction of the electrostatic spray nozzle or other components of the system.
Such spray dryer systems also must be operable for spray drying different forms of liquid slurries. In the flavoring industry, for example, it may be necessary to operate the system with a citrus flavoring ingredient in one run, while a coffee flavoring ingredient is used in the next operation. Residual flavor material adhering to the walls of the drying chamber can contaminate the taste of subsequently processed products. In the pharmaceutical area, of course, it is imperative that successive runs of pharmaceuticals are not cross-contaminated.
Existing spray dryer systems further have lacked easy versatility. It sometimes is desirable to run smaller lots of a product for drying that does not require utilization of the entire large drying system. It further may be desirable to alter the manner in which material is sprayed and dried into the system for particular applications. Still in other processing, it may be desirable that the fine particles agglomerate during drying to better facilitate ultimate usage, such as where more rapid dissolution into liquids with which it is used. Existing sprayers, however, have not lent themselves to easy alteration to accommodate such changes in processing requirements.
Spray dryers further tend to generate very fine particles which can remain airborne in drying gas exiting the dryer system and which must be filtered from gas exiting the system. Such fine particulate matter can quickly clog filters, impeding efficient operation of the dryer and requiring frequent cleaning of the filters. Existing spray dryers also have commonly utilized complex cyclone separation and filter arraignments for removing airborne particulate matter. Such equipment is expensive and necessitates costly maintenance and cleaning.